In recent years, attention has been drawn to a plasma display panel (hereinafter referred to simply as PDP) which has merits such that a large screen panel can be prepared and clear full color display is possible. PDP is to provide a full color display in such a manner that phosphors are selectively discharged to emit light in a large number of discharge cells isolatedly formed between two glass plates.
FIG. 1 is a view illustrating the structure of PDP. In this FIG., PDP shown by reference numeral 1 has a construction in which a front glass 2 and a rear glass 3 are disposed to face each other, and in the space between the two glasses 2 and 3, a rare gas such as xenon is sealed in a reduced pressure state. On the front glass 2, discharge electrodes 4, a dielectric film 5, a protecting film 6, etc. are formed, and on the rear glass 3, partition walls 7, phosphors 8A, 8B, 8C, address electrodes 9, etc. are provided.
The front glass 2 of PDP1 receives scratches or strains at the time of forming or laminating electrodes or thin films made of various materials, and the strength is remarkably deteriorated as compared with the original glass plate. Further, it is in contact with irregularities of the phosphors or the partition walls formed on the rear glass, and the stress is likely to be concentrated at such contact portions.
Heretofore, in order to prevent breakage of the front glass of a flat display panel for e.g. PDP, it has been common to provide a protecting plate made of an acrylic resin or reinforced glass, with a space of a few mm in front of the front glass, to prevent an impact from being exerted to the flat display panel. However, such a protecting structure has had a problem such that it hinders weight reduction or thickness reduction of the flat display panel. Further, there is a space between the protecting plate and the front glass of the panel, whereby there has been a problem such that outside light of e.g. a fluorescent lamp is likely to be reflected to deteriorate the image quality, or the screen image is likely to be distorted by slight vibration.
Various techniques have been proposed to prevent breakage of the front glass of a flat display panel. For example, Patent Document 1 proposes a technique to improve the strength by making the thickness of the front glass thick. However, with this structure, the protecting effect against impact is inadequate, and it increases the weight of the panel, such being problematic.
Further, a structure is proposed in which a protecting plate is bonded to the front glass of a panel via an adhesive layer (e.g. Patent Documents 2 to 5). However, with this structure, the impact is likely to be transmitted to the front glass, and there has been a problem that no adequate effect to prevent breakage of the front glass can be obtained.
As a still another prior art, an impact-reducing laminate (hereinafter referred to as a conventional laminate) is proposed wherein two layers made of transparent synthetic resins i.e. a crack-preventing layer (impact-reducing layer) B and a scatter-preventing layer A thereon, are laminated on the front glass of a flat display panel via a transparent adhesive layer, and the shear modulus of the scatter-preventing layer A is at least 2×108 Pa and the shear modulus of the crack-preventing layer B is within a range of from 1×104 to 2×108 Pa (Patent document 6).
References
Patent Document 1: JP-A-2000-123751
Patent Document 2: JP-A-2000-156182
Patent Document 3: JP-A-11-119667
Patent Document 4: JP-A-11-119668
Patent Document 5: JP-A-11-119669
Patent Document 6: JP-A-2001-266759
However, such a conventional laminate was inadequate in imparting impact resistance to the front glass of e.g. PDP. In Examples in the publication, a so-called “non treated” glass plate having no electrodes or no thin films made of various materials laminated, is used as the glass plate, and the adhesive layer, the impact-reducing layer and the scatter-preventing layer are laminated sequentially thereon, and presence or absence of impact resistance is tested by dropping a hardball thereon. However, as mentioned above, with a real front glass of PDP, as a result of lamination of electrodes or thin films made of various materials, the impact resistance is remarkably deteriorated as compared with non-treated glass and is susceptible to breakage. Therefore, with such a conventional laminate, it has not been proved that adequate impact resistance can be obtained when bonded to the front glass of PDP, of which the impact resistance is substantially deteriorated as compared with a non-treated glass plate.
As described in detail in Examples given hereinafter, in a case where three layers of the same materials and thicknesses as disclosed in Examples of the publication, were laminated on a glass substrate assumed to be the front glass of PDP by forming electrodes and a dielectric film on a glass plate, and the impact resistance was measured by exerting a prescribed impact force by a spring impact, it was found that such a laminate was inadequate in the impact resistance (see Example 23 given hereinafter).
Thus, the conventional laminate was inadequate as an impact resistant film to protect the front glass of a flat display panel such as PDP, having the impact resistance deteriorated.